This invention relates to a toroidal type continuously variable transmission (referred to hereafter as CVT) used in a vehicle or the like, and to a method for manufacturing a trunnion thereof.
Japanese Patent Laying Open Publication Heisei 7-174201 published in 1995 discloses the CVT. In this CVT, mutually opposed power rollers are interposed and held between coaxially disposed input and output disks. Further, trunnions which support the shafts of these power rollers are supported so as to be capable of displacement in the axial direction as well as rotatable around their axes.
With this type of the CVT, the upper ends and the lower ends of the trunnions, which are provided as mutually opposed, are respectively connected together by an upper link and a lower link. Due to this, when a trunnion is displaced along its axial direction, the upper link and the lower link execute swinging movement. At this time, shoulder portions formed upon the trunnions and projecting portions on the upper link or on the lower link may come into contact with one another.
The trunnions are formed by forging. The shoulder portions of the trunnions are formed in predetermined planes by performing a cutting process along the axes of the trunnions.
However, due to dimensional tolerances for the trunnions, it may be the case that the radiuses of the shoulder portions are not equal. Variation may be engendered in each of the trunnions due to sliding resistance caused when the projecting portions and the shoulder portions come into mutual contact. Accordingly, the problem has occurred of hysteresis being engendered in the speed changing characteristic due to variation of the sliding resistance acting in the directions of gyration of the power rollers, which causes deterioration in the accuracy of speed change control.
The objective of the present invention is to prevent the occurrence of hysteresis in the speed change characteristic by rendering uniform the contact condition of the links and the shoulder portions of the trunnions.
In order to achieve above object, this invention provides a toroidal type continuously variable transmission, comprising: a rotation input shaft; an input disk arranged coaxially with the rotation input shaft and is driven thereby; an output disk which is arranged coaxially with the rotation input shaft and opposes said input disks; a pair of trunnions arranged in opposite positions on both sides of the rotation input shaft, each of said trunnions having an axial direction and comprising rotation shafts formed at both end portions of the trunnion, and offset portions which are offset by a predetermined amount from said rotation shafts between the rotator shafts of the trunnions; an actuator which drives each pair of the trunnions in mutually opposite axial direction of the trunnions; power rollers which are supported by said trunnions and are gripped between said input disk and said output disk; links each of which is respectively formed with aperture portions into which said respective rotation shafts of said trunnions are inserted; and spherical joints provided between the outer peripheries of said rotation shafts and said aperture portions; and wherein said trunnions are formed by forging, and shoulder portions of said trunnions which oppose said links and step portions which define outer ends of said shoulder portions are formed by cutting, and said links having projections which contact slidably into said shoulder portions according to swinging movement of said links.
Further this invention provides a method for manufacturing a trunnion of a toroidal type continuously variable transmission, trunnion comprising rotation shafts formed at both ends of said trunnion, and offset portions which connect said rotation shafts with links and locate between said rotation shafts and offset from said rotation shafts; wherein said trunnion is formed by forging, and steps which define the outer ends of said shoulder portions opposing said links are formed in said trunnion by cutting.